§ 132.380 Whom the grand jury may indict

A grand jury has the power to indict anyone it believes committed a crime. It doesn't matter if that person was already arrested, charged, or ordered to face trial before the grand jury looks at the case. The grand jury can act on its own, even if no one has formally accused the person yet.

This means the grand jury isn't limited to just reviewing cases the police or prosecutors already built. If the grand jury finds evidence that someone committed a crime, it can issue an indictment against that person, whether or not they were previously connected to the case in any official way. The key requirement is simply that the grand jury believes, based on the evidence it reviewed, that the person is guilty of the crime.